Dual-functional graphene-modified fibre reinforced cementitious matrix (FRCM) for simultaneous corrosion protection and structural strengthening

The corrosion of embedded steel rebar in reinforced concrete (RC) structures, which are the backbone of every nation's infrastructure, is a major issue. Interventions relating to the corrosion of RC structures are estimated to amount to about 35% of the total volume of all work in the global building sector. Reinforcement corrosion is induced via mobile chloride ions or other structurally harmful contaminates within the reinforced concrete, which happens due to a variety of reasons such as marine environment, de-icing salt in winter seasons, chloride content in concrete mixing and the use of sea sand, etc. With reinforcement corrosion, the load-bearing resistances of RC structures are reduced, with severe potential safety issues and also immense economic loss.

A new intervention method, ICCP-SS (impressed current cathodic protection and structural strengthening), has recently been proposed. ICCP-SS combines the merits of impressed current cathodic protection (ICCP) and structural strengthening (SS) technologies, but uses one dual-functional material - carbon fibre reinforced cementitious matrix (C-FRCM). In this dual functional material, the carbon fibre (CF) mesh serves as the anode for ICCP and also the strengthening material for SS, while the cementitious matrix is the conductor for ICCP and the bonding material for SS. Previous studies have demonstrated effectiveness of the ICCP-SS technology for RC members. However, it has been found that prolonged ICCP would cause calcium leaching in the cementitious matrix at the anode interface, leading to drastic loss of mechanical properties and significant increase of electrical resistance of the bond between the cementitious matrix and CF mesh.

Reducing calcium leaching to a level that does not adversely affect structural resistance is possible by increasing the compactness and the electrical conductivity of the cementitious matrix to achieve a more uniform electrical resistive field in the anode interface; introducing a tiny amount of graphene into the cementitious matrix has the potential to do so. The key to solving the problem is to prevent (or significantly slow down) the breakdown of C-S-H gel (i.e. loss of calcium) at anode interface under the same ICCP current density and duration. The remarkable properties of graphene make it a potentially ideal solution to this problem by producing a more uniform electrical field and more compact microstructures of the cementitious matrix.

This project aims to solve two issues: to quantify the bond mechanical behaviour (for SS) and the electrical resistance at the CF/cementitious matrix interface (for ICCP) due to leaching, and to investigate means of reducing leaching. In summary, the ICCP-SS intervention method has vast potential in prolonging life of RC structures and introducing a small amount of graphene flakes in the dual-functional cementitious matrix has a number of beneficial synergistic effects to help realise the full potential of ICCP-SS.

Discussions with our industrial stakeholders have confirmed that we are breaking new scientific ground with DualFRCM whilst demonstrating also an understanding of the many challenges of improving the performance of cementitious matrix with graphene. They are also optimistic of our proposed ICCP-SS intervention methods using the dual-functional graphene-modified FRCM for future applications and readiness (see letters of support). The broad scope of this project means there is a wide range of beneficiaries and stakeholders who will be impacted throughout this project and beyond and our pathways to impact are designed to reach these beneficiaries effectively at the earliest opportunity. The case for support highlights examples of how graphene-modified FRCM can deliver cost avoidance, cost reduction and reduced resource footprint and lower environmental impact. The application of the proposed intervention method will potentially reduce the energy consumption and carbon footprint.

The main beneficiaries and impacts include:
- Graphene manufacturers and suppliers: opportunities of application of their materials in the traditional construction industry.
- Cement and concrete manufacturers: production of high-performance construction and building materials with new nanomaterials (such as graphene, graphene oxide, carbon nanotube etc.) with lower carbon footprint.
- Construction consultants and contractors: new intervention method for improving reinforced concrete infrastructure subjected to corrosion.
- Property owners: new intervention method with cost and energy saving for degraded properties.
- Regional government: improved performance and extended service life of existing infrastructure (such as bridges); budget saving for repair of degraded structures.
- Regulators: guidance on graphene-modified construction materials - uptaking and upscaling of innovation.
- Central government and wider policy environment: new and improved method of improving infrastructure durability and applying sea sand resource.
- British/European Standards committee: new intervention method for codification
- General public: improved safety and resilience of infrastructure, reduced environmental impacts.
- Younger generations: to inspire the younger generation especially women for future scientific studies and careers.